The present invention encompasses methods for saponifying organic acid esters, including fatty acid glyceride esters. More specifically, organic acid esters are saponified using a concentrated aqueous solution of sodium hydroxide or lithium hydroxide in a liquid reaction medium comprising an alkyl nitrile to provide partially solvated, yet solid, filterable sodium or lithium metal salts of the organic acids. When fatty acid esters are used in the process, soaps and lubricating greases are secured.
The preparation of alkali metal salts of organic acids by saponifying the corresponding organic acid esters, as in traditional soap making processes, is typically carried out using an alkali metal hydroxide base, the organic acid ester, and water as the reaction medium. Heretofore, such reactions have been energy intensive for at least two reasons. First, heat energy is required to initiate and sustain the saponification of the organic acid ester by the aqueous solution of the alkali metal hydroxide. Second, the organic acid salts are strongly solvated by the water from the aqueous reaction medium. Accordingly, some of the water must be removed to recover the organic acid salts, and heat energy is needed for this solvent removal step. Moreover, the soaps prepared in water are in a sticky, intractable, non-crystalline state and cannot be recovered by simple filtration processes.
The co-pending application of Peterson, entitled SOAP MAKING, Ser. No. 731,183, filed Oct. 12, 1976, teaches that substantially anhydrous alkyl nitriles provide a reaction medium wherein organic acid esters can be saponified with alkali metal hydroxides to provide the alkali metal salts of organic acids which precipitate from the reaction medium in an unsolvated form. Accordingly, solvent removal is not a high energy consuming step in the disclosed process. Moreover, the Peterson process is exothermic and, once initiated, proceeds substantially to completion without external heating. Soap making processes carried out by the Peterson process using fatty glycerides as the organic acid ester provide substantially dry, unsolvated, crystalline, filterable white soap powder in an extremely short period of time in exceptionally high yields.
It has now been determined that the basic Peterson process for making soap can be modified to employ concentrated aqueous solutions of sodium hydroxide or lithium hydroxide, thereby facilitating handling. Moreover, concentrated solutions of these alkali metal hydroxides are relatively inexpensive articles of commerce, as compared with their solid form. By controlling the total amount of water introduced into the alkyl nitrile medium in the syrupy, concentrated hydroxide solution, solid, yet partially hydrated, filterable white powders comprising the alkali metal salts of fatty acids are still secured.
If excessive amounts of water are used in the present process, the special advantages are lost and the reaction proceeds in much the same manner as wet process soap manufacture, with the formation of viscous masses of the fatty acid salts or soaps at reduced reaction rates. Indeed, with alkali metal hydroxides such as KOH, RbOH and CsOH, intractable, tacky soaps are secured in the presence of even small (greater than about 10%) amounts of water in the total reaction system. Accordingly, preparation of the soaps of these latter alkali metals is preferably carried out via the anhydrous Peterson process, mentioned above, and aqueous solutions of KOH, RbOH or CsOH are not used in the practice of the present invention.